Abrasive blasting unit

ABSTRACT

An abrasive blasting unit includes a movable transporter upon which is mounted a vertical tower with a work platform secured to the tower in such a manner that the platform can be raised up and down the tower. A boom is pivotally connected to the platform and has an abrasive blast wheel connected at its remote end while conveying elements are incorporated in the boom for feeding abrasive particles to the blasting unit.

D United States Patent 11 1 1 11 3,747,277 Carpenter et al. 1 July 24, 1973 [54] ABRASIVE BLASTING UNIT 3,262,228 7I l966 Schenck 51/9 1 1 w 8 3'33??? 111323 2222353.;131111113: 233

Md.; Harper Willard Good, W b aynes om Pa Primary Examiner-Donald G. Kelly [73] Assignee: The Carborundum Company, AttorneyDavid E. Dougherty and Robert E.- Walter Niagara Falls, N.Y. [22] Filed: Apr. 12, 1971 57 ABSTRACT PP N05 133,272 An abrasive blasting unit includes a movable transporter upon which is mounted a vertical tower with a [52] US. Cl. 51/9 work Platform secured to'the tower in Such a manner [51] Int C| n B24: 3106, B240 3/32, B24c 7/00 that the platform can be raised up and down the tower. 58 Field of Search 51/8, 9 180 A is P the Platfmm and has I an abrasive blast wheel connected at its remote end [56] References Cited while conveying elements are incorporated in the boom UNITED STATES PATENTS for feeding abrasive particles to the blasting unit. 3,566,543 '2/1968 Fogle 51/9 14 Claims, 9 Drawing Figures rs i ez 1' Ii 1 22 5 30 T71". I 86 9O ABRASIVE BLASTING UNIT BACKGROUND OF INVENTION This invention relates to an abrasive blasting unit particularly to such a unit which is adapted to the blast cleaning of ship hulls.

Ships must be periodically placed in drydock so as to permit re-conditioning of the hull. Paint, scale, barnacles and other debris mustbe removed before the hull is repainted. Present methods involve blasting the surface manually by the use of nozzles which direct abrasive particles against the side of the ship by means of air pressure. The abrasive and other debris fall through the air to the floor of the drydock. The result is complete loss of all the abrasive, air pollution and presence of several inchesof debris on the drydock floor and surrounding areas as wellas an exorbitant amount of down time and expensive repairs due to entrance of the abrasive and associated foreign particles in electrical and mechanical components.

SUMMARY OF INVENTION An object of this invention is to provide an abrasive blasting unit which overcomes the above disadvantages.

A further object of this invention is to provide such a blasting unit wherein air pollution becomes virtually nil by having the abrasive and debris collected, separated and stored so that very little foreign matter enters the air.

A still further object of this invention is to provide such an abrasive blasting unit wherein by separating the abrasive from the debris the abrasive may be continuously recycled until it is no longer usable. Accordingly, the drydock floor is kept clean which contributes to safety and reduced fire hazard, as well as good housekeeping.

A still further object of this invention is to provide such an abrasive blasting unit which utilizes an airless process by throwing abrasive particles at high velocity against the side of the ship so that the surface cleaning may be accomplished many times faster than by the conventional methods. Thus many man hours are saved and the cost of having a ship in drydock is greatly reduced. Moreover, the resultant finish is much better than when done by the manual method thereby preparing the surface for greatly increased paint adhesive qualities. As a result a substantially dollar savings can be realized by reduced down time and repair of parts which are presently affected by abrasive contamination, and the cost of cleaning up a ship after such an operation would be minimized. Furthermore human safety would also be benefited since only one person is required to operate the abrasive blasting unit whereas the operator will not be subjected to the hazards of air pollution or flying abrasives.

A still yet further object of this invention is to provide such an abrasive blasting unit which is portable and self-contained.

In accordance with this invention an abrasive blasting unit includes a movable transporter upon which is mounted a vertical tower with a work platform secured to the tower in such a manner that the platform can be raised up and down the tower. A boom is pivotally connected to the platform and has an abrasive blast wheel connected at its remote end while conveying means are incorporated in the boom for feeding abrasive particles to the blasting unit.

The boom may also include second conveying means for transporting spent abrasive particles and refuse away from the wheel. The tower may be mounted on an auxiliary car which in turn is movably mounted on the transporter whereby the tower and platform may traverse the transporter.

The boom may comprise upper and lower hollow structural members which are interconnected to each other with each member pivotally mounted to the platform and with the blast wheel pivotally mounted to the upper member. The various pivot means may be in the form of hollow shafts which communicate with screw conveyors in each of the upper and lower structural members and with the blast wheel. The blast wheel may also be mounted for movement about a horizontal axis and the lower structure member may include an'open spout communicating with its screw conveyor and disposed under the blast wheel for catching falling spent abrasive and refuse regardless of the position of the blast wheel. The blast wheel may be mounted in a housing which also includes a shroud for confining the abrasive'particles with an opening being provided in the shroud for contacting the ship hull. The opening may be surrounded by sealing lips for pressing against the ship hull to conform to its contour.

THE DRAWINGS FIG. 1 is a side view in elevation of an abrasive blasting unit in accordance with this invention;

FIG. 2 is a top plan view of the abrasive blasting unit shown in FIG. 1;

FIG. 3 is a side view in elevation similar to FIG. 1 showing the unit in a different phase of operation;

FIG. 4 is a front view in elevation of the unit shown in FIG. 3 in different phases of operation;

FIG. 5 is a plan view of the unit shown in FIG. 4;

FIG. 6 is a cross-sectional view in elevation illustrating the telescopic tower construction;

FIG. 7 is a cross-sectional view taken along the lines 7-7 of FIG. 3;

FIG. 8 is a side view in elevation schematically show ing different positions of the blasting unit; and

FIG. 9 is a top plan view schematically showing different positions of the blasting unit.

DETAILED DESCRIPTION As illustrated in the drawings the abrasive blasting unit 10 includes a movable transporter or carriage 12 upon which is mounted an auxiliary car 14. Secured to car 14 is a vertical tower 16 while a work platform 18 is connected to the tower in such a manner that the platform may be elevated up or down the tower. In this respect platform l8.includes a sleeve 19 which telescopes over tower l6. Attached to the platform is a boom 20 with an abrasive blast wheel assembly 22 secured thereto. The boom, as later described, includes steering of these two wheels. All of the wheels are mounted on pneumatic tires which may be equipped with suitable blow-out protection for the interest of safety. The wheels may be hydraulically or electrically powered and may be equipped with brakes. A selfretracting electrical cable reel 28 may provide power for the machine as well as for movement of the total machine during the normal process of operation. In a form of this invention which is particularly designed for ship hull cleaning the cable reel may have 200 feet capacity. To provide stability for the unit during use, a

plurality of outriggers 30 are mounted on the transporter or carriage 12 at the four corners thereof to virtually raise the entire unit off the rubber tires (FIG. 3) and to permit leveling of the carriage 12. In this respect the outriggers may be hydraulically extended and may be provided with lifting pads 31 as well as mercury switch leveling controls to assure proper vertical positioning of the entire unit.

Auxiliary car 14 is provided with a plurality of rollers 32 which ride in tracks 34 provided on transporter or chassis 12 so that the tower l6 and its work platform 18 may traverse the transporter 12. FIG. 3, for example, illustrates the tower in full lines in one position of traversal and in broken lines in another position of traversal. The rollers 32 are restricted on both top and bottom thereof to prevent the platform from tipping out of position during operation.

Platform 18 contains a recessed well in its central area to accommodate tower 16. Tower 16 is constructed of telescopic columns including fixed vertical column 36 which may have for example a height of about 38 feet. Column 36 is preferably rectangular in cross-section and is open at its top. Completely encasing column 36 similar to a cap is a second column 38 (FIG. 6). Column 38 is free to move vertically upward to, for example, 68 feet high while platform 18 includes a sleeve 19 telescopically mounted around column 38 for movement up and down this column. Any suitable elevating means may be used to actuate the telescopic tower and to elevate and lower platform 18. For example, as shown in FIG. 6 a dual set of lifting apparatus permits outer column 38 to move vertically from a height of, for example, 38 feet to 68 feet. This lifting apparatus includes a pair of rack and pinion arrangements 40 which react between columns 36 and 38. Thus if one of the arrangements 40 should fail the tower would be held in position by the other arrangement. As illustrated in FIG. 6 the rack and pinion arrangements 40 include a pinion 42 mounted on the end of hydraulic cylinder 44 for moving column 38 by means of racks 46, 48 on both sides of the pinion. Alternatively, a winch may also be used as an elevating means as well as any other suitable arrangements.

Similarly platform 18 may be elevated in any suitable manner. Thus as shown in FIGS. 3 and 6 the platform elevating means may include a pair of chains 50 secured to the sleeve 19 of platform 18 at suitable locations 52, with the chains being disposed over pulleys 54 which are driven by motor 56.

As previously indicated auxiliary car 14, tower 16 and platform 18 are provided with means for traversing transporter 12. This means may include a hydraulic piston-cylinder arrangement 58 which reacts between auxiliary car 14 and transporter 12 in such a manner that upon extension of the piston rod 60 the tower is in the position indicated in broken lines in FIG. 3, while upon retraction of piston rod 60 the tower is in the position indicated in full lines.

A suitable pump assembly 45 is mounted on transporter 12 for supplying hydraulic fluid to cylinders 44 and 58 and outriggers 30.

The tower elevating means, the auxiliary car traversing means and the platform elevating means are preferably interlocked in such a manner that the transporter 12 is inactivated unless the platform 18 is in its lowermost position. Also, the tower elevating means is inactivated unless the platform 18 is in its uppermost position with respect to column 38. Thus, the interlocking means prevents upward movement of the telescopic columns 36 and 38 until the platform 18 is at the top of column 38.

In an advantageous form of this invention the transporter traversing means enables the platform and its tower to move horizontally for example 7 feet along the longitudinal axis of the transporter frame in preselected increments commensurate with the width of the blast pattern from blasting wheel assembly 22. In operation the blast platform 18 moves vertically along outer column 38 until it reaches its maximum height. If this height is insufficient with respect to the height of the ship hull outer column 38 may be extended upwards until the desired height is reached. Obviously if two columns are insufficient to obtain the desired height any number of telescopic columns may be provided. When the movable platform 18 has reached its desired height it is moved horizontally on transporter 12 one increment and the column 38 is then lowered at a controlled rate of speed carrying with it the blast cleaning assembly 22. In this manner the blast cleaning assembly is capable of producing four vertical blast trips (i.e., two trips up and two trips down) based upon the exemplary dimensions of the unit, before it is necessary to relocate the main transporter. Additional trips can be provided at a sacrifice to transporter length. The illustrated transporter 12 is capable of operating within about an 8 foot width and about a 38 feet length while the column and equipment can extend to a maximum of about feet height and can collapse to a minimum of about 40 feet height. The illustrated blast unit assembly is designed to blast from about 6 feet minimum to about 60 feet maximum height. Advantageously, to maintain the unit self-contained hydraulic pumps 45 are provided to operate the outriggers both vertically and horizontally with the hydraulic oil supply being stored in the frame of the transporter 12.

Blast platform 18 advantageously incorporates the blast wheel assembly and its related equipment. As previously described platform 18 rides up and down outer column 38 by being suspended by two cables or roller chains 50. Preferably one chain or cable is sufficient to hold the weight involved with a pair being provided as a safety feature. The motor winch 56 raises and lowers the platform. The various controls for the unit are provided at a sheltered operator's station 62 to raise and lower the column and blast platform and to perform all functions in connection with the blasting operation as well as movements of the transporter.

As shown in FIG. 7 blast wheel assembly 22 consists of a small diameter head 64 containing several vanes which throw abrasive particles at high speed against the ship hull H. The blast wheel 66 which may be of any suitable construction generally has a vertical axis and is mounted directly to a high speed motor 68 with the assembly housing including a shroud 70 to retain abrasive particles within its confines. Shroud 70 includes an opening 72 disposed toward ship hull H. The opening is provided with sealing lips 71 such as triple abrasive seals made of rubber and of stainless steel wire brushes to prevent abrasive from flying outside the shroud. The whole assembly 22 is held against hull H by hydraulic pressure. For this purpose sensors 76 automatically and continuously insure that this pressure will be maintained at all times while blasting. The lip structure and sensors also assure that the wheel 66 will be kept orientated with respect to the contour of the blasted surface which is particularly important since, as later described, wheel assembly 22 is free to pivot on both horizontal and vertical axes. In this respect wheel assembly 22 is mounted on a rotatable shaft 78 rotatably secured to boom 20 with suitable bearings 81) being provided. As later described shaft 78 is hollow so that abrasive particles can be fed from the hollow interior of upper structural member 82 of boom 20 through slide valve 121 which provides for abrasive shut'off and variable abrasive flow. A pivot joint 84 is also provided on a yoke to permit limited movement about a horizontal axis. Instead of a yoke, an L-shaped member may be used. Preferably the movement about a vertical axis is approximately i 90 while movement about the horizontal axis is a tilt 45 up from the horizontal position and a tilt of down from the horizontal position as indicated by the reference letters a and b in FIG. 7.

As shown in FIGS. 3 and 7 boom includes a lower structural member 86 which is hollow and which is provided with an open inverted conically shaped spout 88 for receiving the falling mixture of spent abrasive particles and refuse which is discharged through opening 90 of shroud 70. Since spout 88 is provided with an enlarged open top, communication with opening 911 is maintained regardless of the adjusted position of blast wheel assembly 22.

As previously indicated boom 211 is in the form of an upper hollow structural member $2 and a lower hollow structural member 86 which are interconnected by any suitable means such as beams 92, 94. Structural members 82, 86 are pivotally secured to platform 18 by coaxial hollow shafts 96, 98, respectively. These shafts serve the multiple functions of supporting the boom as well as providing the pivot means therefor and also providing feed means. In an advantageous form of this invention the overall length of boom 20 is about 14 feet and the provision of the pivot means near vertical column 38 allows blast wheel assembly 22 to blast a surface which is about 12 feet away from the normal blasting position. Advantageously, structural member 82 houses or encloses a screw conveyor 100 (FIGS. 1 and 7) for feeding abrasive particles to the blast wheel 66. Since the hollow pivots are of open construction abrasive may be fed to the screw conveyor through hollow shaft 96 which communicates with the interior of structural member 82. This open pivot design facilitates a resultant simplified and compact unit. Similarly, a second screw conveyor 102 is provided in lower structural member 86 for receiving the mixture from spout 88 and transporting it away from blast wheel assembly 22. As shown in FIG. 1 the mixture is discharged from screw conveyor 102 through its hollow shaft 98 into a further screw conveyor 104 on platform 18. From screw conveyor 104 the mixture is discharged into elevator 106 and is conveyed to a suitable separator 1118 and scalping drum assembly. The separator is preferably of the air wash type where the mixture is divided into its individual components. Thus separator 108 includes means for collecting coarse refuse as well as fine refuse. The

.dust from separator 103 is conveyed through duct 110 into dust collector 112. Additionally, substantially pure abrasive particles are also separated in separator 108 and are fed into hopper 11 1 and metered through gate where it is lifted, by elevator 116 for recirculation through screw conveyor 122 to hollow shaft 96 and screw conveyor 100 and back into blast wheel assembly 22.

A flexible duct is provided between dust collector 112 and blast wheel assembly 22 to purge the air in the wheel housing area with the dust from this area being fed to the dust collector. For the sake of clarity only portions 11%, 118 of the duct are illustrated in FIG. 2. Any suitable dust collector may be used. In a preferred form of this invention a commercially available filter tube dust collector is employed which uses a minimum of auxiliary air to perform its function. The dust is collected in hopper 1211 which is periodically emptied. Similarly the fine and coarse refuse bins are also periodically emptied. Additionally, in use care is taken to asure that the abrasive supply is adequate.

As previously indicated suitable interlocks and safety devices assure proper operation of unit 10. Thus, for example transporter 12 cannot be operated until blast platform 18 is in its lowest position. Additionally, the front and rear wheels cannot be actuated in such a manner as to oppose each other. Furthermore, blast platform 1% cannot be actuated until the outriggers 30 have raised the wheels 24, 26 off the floor. Moreover, blast wheel 66 will automatically stop if adequate pressure against the ship hull H is not maintained. In this respect sensors 76 may cause gate valve 121 to close when there is insufficient pressure.

Blasting unit 11) thereby provides a versatile unit which is suitable for cleaning the various irregular and relatively inaccessible contours encountered in a ship hull. FIGS. 4, 8 and 9 are exemplary of the various positions which may be obtained by the blasting assembly 22 with respect to the drydock D and hull H for an effective cleaning operation.

The-following is one example of the use of unit 10. The operator at the control station is capable of moving the entire unit into its starting position by steering the carriage and transporter into location. The blast positioning mechanism is at this time fully retracted and in a location swung parallel to the transporter and ships hull and forward of the tower. Once the transporter is in the required position at approximately 2 feet 6 inches from the center line of blast boom to the straight vertical side of the hull or its farthest extending protrusion, overhang, etc., the operator extends the pivotable outrigger support arms 30 to suitable open spaces on the graving dock floor. The outriggers 31) are arranged thusly, to allow their extension to spaces inbetween the blocking system underneath the ships hull.

The hydraulically activated lift and support pads 31 at the end of the outriggers 311 are now engaged from the control station to lift the transporter carriage 12, tower 16 and blast platform 1% off the pneumatic tires. The operator adjusts the transporter 12 to a level position by means of a level indicator and associated controls. The unit is now safely positioned to start the blast cleaning cycle.

From the same operating station the operator can perform all control functions necessary to move the blast head 22 through its motions at the hull H, including up and down motion of blast platform 18 and telescoping tower 16, movement of the blast head 22 against the contour of the hull H, auxiliary longitudinal tower movement along the transporters tower base and the activation of the wheel, abrasive handling system, separator and dust collector.

The blast head 22 is then swung out against the hull H and the head is adjusted to confonn to the contour. The tower is at this time at its farthest position towards the rear of the transporter with the blast platform at its lowest position.

The operator selects a suitable blasting speed and engages the abrasive feed system. As blast head 22 and platform 18 move up vertically on the lower portion of the tower structure, sensing switches 76 at the blast head maintain its orientation against the hulls contour in order to also maintain a seal of the blasting chamber at the hull. While blasting a vertical swath of approximately 23 inches wide, the platform approaches the top of the lower tower structure and the tower automatically extends at the preselected blasting speed with the blasting platform locked into position at the upper portion of the extending tower.

The operator riding at the upper portion of the tower in station 62 is therefore able to easily stop blast action and upward motion as he reaches hull obstructions.

Having reached the upper limits of his blast cycle, the operator moves the entire tower on its transporter base alongside the hull until the blast head is relocated to engage blasting the second swath and a downward motion. In this fashion it is possible to blast clean an approximately 9 feet wide area without having to move the transporter.

The final swath of the 9 foot area is blasted in a downward motion and the blast platform is again at its lowest position with the tower at its collapsed height.

The tower is then moved on its carrier base to the rear position of the transporter and the blasting head is retracted. The lift pads then lower the transporter onto its pneumatic tires, the outriggers 30 are retracted and the transporter 12 is moved to a new position alongside the hull H in preparation for blast cleaning another 9 foot wide area.

As is readily apparent blasting unit provides a number of distinct advantages. These advantages include: reclamation of abrasive with its money-saving aspects; control of air pollution; less down-time due to failure of equipment resulting from abrasive contamination; less man-power required; greater safety for workmen in the area; less expensive ship clean-up operation after blast cleaning; greatly increased production; less time required for drydock service; more consistent results incleaning the metal surface; less time and work involved in setting up for blasting; and cleaner drydock floor and surrounding area.

What is claimed is:

1. An abrasive blasting unit comprising a movable transporter, a vertical tower mounted on said transporter, a work platform, elevating means connecting said platform to said tower for movement up and down said tower, a boom pivotally connected to and extending outwardly from said platform, an abrasive blast wheel connected to said boom remote from said platform, and said boom incorporating first conveying means for feeding abrasive particles to said blast wheel.

2. A blasting unit as set forth in claim 1 wherein said boom incorporates second conveying means for transporting spent abrasive particles and refuse away from said wheel.

3. A blasting unit as set forth in claim 2 wherein said tower is mounted on an auxiliary car, and roller means movably mounting said auxiliary car on said transporter whereby said tower and said platform may traverse said transporter.

4. A blasting unit as set forth in claim 3 wherein said boom comprises upper and lower hollow structural members interconnected to each other, said blast wheel being mounted in a housing, said housing being mounted by pivot means to one end of said upper structural member, said first conveying means being a screw conveyor in said upper structural member, pivot means connecting the other end of said upper member to said platform for pivotal movement about a vertical axis, one end of said lower structural member being disposed under said blast wheel for receiving the falling spent abrasive and refuse, said second conveying means being a screw conveyor in said lower structural member, and pivot means connecting the other end of said lower structural member to said platform for pivotal movement about a vertical axis.

5. A blasting unit as set forth in claim 4 wherein said tower comprises a plurality of telescopic columns, and said blast wheel being mounted for pivotal movement about a horizontal axis.

6. A blasting unit as set forth in claim 5 wherein said pivot means for said upper and lower members comprises a hollow rotatable shaft the interior of which communicates with its screw conveyor to permit abrasive particles to pass therethrough.

7. A blasting unit as set forth in claim 6 wherein said blast wheel housing includes a shroud to confine the abrasive particles, an opening in said shroud to permit abrasive particles to be projected against an object to be cleaned, and sealing lips around said opening for permitting the housing to press against the object to be cleaned.

8. A blasting unit as set forth in claim 7 wherein said platform includes an operator's station, said blast wheel being directly mounted to a motor shaft, said lips incorporating sensor means to maintain said lips in contact with the object to be cleaned and to orient said wheel with respect to the contour of the object to be cleaned, an open receiving spout connected to said lower member under an opening in said shroud to permit said shroud and said wheel to pivot while receiving the falling spent abrasive and refuse, said spout communicating with said second screw conveyor, a first elevator on said platform communicating with the second screw conveyor for receiving a mixture of spent abrasive and refuse therefrom, a separator on said platform comm unicating with said first elevator for separating the mixture into its components including substantially pure abrasive particles, and a second elevator on said platform communicating with said separator for feeding the substantially pure abrasive particles to said first screw conveyor.

9. A blasting unit as set forth in claim 8 wherein a feed hopper is mounted on said platform communicating with said separator for receiving the substantially pure abrasive particles therefrom, said second elevator communicating with said feed hopper, a dust collector being mounted on said platform, said dust collector communicating with said separator, and a flexible duct communicating with the interior of said shroud and with said dust collector to purge the air therefrom.

10. A blasting unit as set forth in claim including interlocking means for preventing upward movement of said telescopic columns until said platform is at the top .of its column.

11. A blasting unit as set forth in claim 3 wherein said roller means comprises a plurality of rollers mounted on said auxiliary car, track means on said transporter, said rollers being mounted in said track means, and means on both the top and bottom of said rollers to prevent said platform from tipping.

12. A blasting unit as set forth in claim 11 including platform. 

1. An abrasive blasting unit comprising a movable transporter, a vertical tower mounted on said transporter, a work platform, elevating means connecting said platform to said tower for movement up and down said tower, a boom pivotally connected to and extending outwardly from said platform, an abrasive blast wheel connected to said boom remote from said platform, and said boom incorporating first conveying means for feeding abrasive particles to said blast wheel.
 2. A blasting unit as set forth in claim 1 wherein said boom incorporates second conveying means for transporting spent abrasive particles and refuse away from said wheel.
 3. A blasting unit as set forth in claim 2 wherein said tower is mounted on an auxiliary car, and roller means movably mounting said auxiliary car on said transporter whereby said tower and said platform may traverse said transporter.
 4. A blasting unit as set forth in claim 3 wherein said boom comprises upper and lower hollow structural members interconnected to each other, said blast wheel being mounted in a housing, said housing being mounted by pivot means to one end of said upper structural member, said first conveying means being a screw conveyor in said upper structural member, pivot means connecting the other end of said upper member to said platform for pivotal movement about a vertical axis, one end of said lower structural member being disposed under said blast wheel for receiving the falling spent abrasive and refuse, said second conveying means being a screw conveyor in said lower structural member, and pivot means connecting the other end of said lower structural member to said platform for pivotal movement about a vertical axis.
 5. A blasting unit as set forth in claim 4 wherein said tower comprises a plurality of telescopic columns, and said blast wheel being mounted for pivotal movement about a horizontal axis.
 6. A blasting unit as set forth in claim 5 wherein said pivot means for said upper and lower members comprises a hollow rotatable shaft the interior of which communicates with its screw conveyor to permit abrasive particles to pass therethrough.
 7. A blasting unit as set forth in claim 6 wherein said blast wheel housing includes a shroud to confine the abrasive particles, an opening in said shroud to permit abrasive particles to be projected against an object to be cleaned, and sealing lips around said opening for permitting the housing to press against the object to be cleaned.
 8. A blasting unit as set forth in claim 7 wherein said platform includes an operator''s station, said blast wheel being directly mounted to a motor shaft, said lips incorporating sensor means to maintain said lips in contact with the object to be cleaned and to orient said wheel with respect to the contour of the object to be cleaned, an open receiving spout connected to said lower member under an opening in said shroud to permit said shroud and said wheel to pivot while receiving the falling spent abrasive and refuse, said spout communicating with said second screw conveyor, a first elevator on said platform communicating with the second screw conveyor for receiving a mixture of spent abrasive and refuse therefrom, a separator on said platform communicating with said first elevator for sEparating the mixture into its components including substantially pure abrasive particles, and a second elevator on said platform communicating with said separator for feeding the substantially pure abrasive particles to said first screw conveyor.
 9. A blasting unit as set forth in claim 8 wherein a feed hopper is mounted on said platform communicating with said separator for receiving the substantially pure abrasive particles therefrom, said second elevator communicating with said feed hopper, a dust collector being mounted on said platform, said dust collector communicating with said separator, and a flexible duct communicating with the interior of said shroud and with said dust collector to purge the air therefrom.
 10. A blasting unit as set forth in claim 5 including interlocking means for preventing upward movement of said telescopic columns until said platform is at the top of its column.
 11. A blasting unit as set forth in claim 3 wherein said roller means comprises a plurality of rollers mounted on said auxiliary car, track means on said transporter, said rollers being mounted in said track means, and means on both the top and bottom of said rollers to prevent said platform from tipping.
 12. A blasting unit as set forth in claim 11 including piston-cylinder means connected between the auxiliary car and said transporter to permit said auxiliary car to transverse said transporter.
 13. A blasting unit as set forth in claim 1 wherein a front wheel and a pair of rear wheels are mounted under said transporter, each of said wheels having self-contained drives and being steerable + or - 90*, and said rear wheels being interlocked to prevent opposed steering thereof.
 14. A blasting unit as set forth in claim 12 including a plurality of outriggers connected to said transporter for stabilizing said transporter and for leveling said platform. 